U.S. patent number 8,376,548 [Application Number 12/887,572] was granted by the patent office on 2013-02-19 for near-eye display with on-axis symmetry.
This patent grant is currently assigned to Vuzix Corporation. The grantee listed for this patent is Robert J. Schultz. Invention is credited to Robert J. Schultz.
United States Patent |
8,376,548 |
Schultz |
February 19, 2013 |
Near-eye display with on-axis symmetry
Abstract
A near-eye display projects virtual images from an image
generator to an eyebox within which the virtual images can be seen
by a viewer. A first optical path conveys image-bearing light from
the image generator to a selectively reflective powered optic and a
second optical path conveys the image-bearing light along a line of
sight from the selectively reflective powered optic to the eyebox.
First and second selectively reflective surfaces fold the first
optical path with respect to the second optical path to locate the
image generator out of the line of sight to the eyebox. The image
generator is effectively inclined to the line of sight to the
eyebox for reducing a thickness of the near-eye display. The
selectively reflective powered optic is oriented normal to local
overlapping portions of the first and second optical paths at the
selectively reflective powered optic.
Inventors: |
Schultz; Robert J. (Farmington,
NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
Schultz; Robert J. |
Farmington |
NY |
US |
|
|
Assignee: |
Vuzix Corporation (Rochester,
NY)
|
Family
ID: |
45817532 |
Appl.
No.: |
12/887,572 |
Filed: |
September 22, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20120069413 A1 |
Mar 22, 2012 |
|
Current U.S.
Class: |
353/10; 359/479;
359/13; 359/247; 359/22; 359/15; 349/11; 353/98; 353/20 |
Current CPC
Class: |
G02B
5/32 (20130101); G02B 27/0101 (20130101); G02B
2027/0112 (20130101) |
Current International
Class: |
G03B
21/14 (20060101); G02B 27/22 (20060101); G02B
5/32 (20060101); G03B 21/28 (20060101); G03H
1/26 (20060101); G02F 1/1335 (20060101); G02F
1/07 (20060101); G02F 1/03 (20060101) |
Field of
Search: |
;353/10,20,98-99
;359/15,13,22,247,479 ;349/11 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Epps; Georgia Y
Assistant Examiner: Cruz; Magda
Attorney, Agent or Firm: Salai, Esq.; Stephen B. Ryan,
Patent Agent; Thomas B. Harter Secrest & Emery LLP
Claims
The invention claimed is:
1. A near-eye display for projecting virtual images from an image
generator to an eyebox within which the virtual images can be seen
by a viewer comprising a selectively reflective powered optic
connecting first and second optical paths, the first optical path
providing for conveying image-bearing light from the image
generator to the selectively reflective powered optic and the
second optical path providing for conveying the image-bearing light
along a line of sight from the selectively reflective powered optic
to the eyebox, first and second selectively reflective surfaces
folding the first optical path with respect to the second optical
path to locate the image generator out of the line of sight to the
eyebox, the image generator being effectively inclined to the line
of sight to the eyebox for reducing a thickness of the near-eye
display, and the selectively reflective powered optic being
oriented normal to local overlapping portions of the first and
second optical paths at the selectively reflective powered
optic.
2. The near-eye display of claim 1 in which the image generator is
oriented normal to a local portion of the first optical path at the
image generator.
3. The near-eye display of claim 2 in which the first selectively
reflective surface and the selectively reflective powered optic
have optical axes oriented substantially parallel to the line of
sight along the second optical path and the second selectively
reflective surface has an optical axis oriented with respect to the
axis of the first selectively reflective surface through an angle
of less than 45 degrees.
4. The near-eye display of claim 3 in which the second selectively
reflective surface is oriented with respect to the first
selectively reflective surface through an angle between 25 degrees
and 35 degrees.
5. The near-eye display of claim 1 in which the image generator or
a relayed image of the image generator is inclined to the line of
sight to the eyebox.
6. The near-eye display of claim 1 in which the first selectively
reflective surface conveys the image-bearing light by at least one
of reflection and transmission at different points along the first
optical path from the image generator to the selectively reflective
powered optic and conveys image-bearing light by transmission along
the second optical path from the selectively reflective powered
optic to the eyebox.
7. The near-eye display of claim 6 in which the second selectively
reflective surface that conveys the image-bearing light by
reflection along the first optical path from the image generator to
the selectively reflective powered optic and by transmission along
the second optical path from the selectively reflective powered
optic to the eyebox.
8. The near-eye display of claim 1 in which the selectively
reflective powered optic is a holographic optic arranged for
focusing the image-bearing light and transmitting ambient light
along the line of sight to the eyebox.
9. The near-eye display of claim 8 in which the second selectively
reflective surface includes a polarization-sensitive beamsplitter
and a polarization modifier is located between the first
selectively reflective surface and the selectively reflective
powered optic.
10. The near-eye display of claim 9 in which the first and second
selectively reflective surfaces are unpowered optical surfaces.
11. A near-eye display for projecting virtual images from an image
generator to an eyebox within which the virtual images can be seen
by a viewer comprising a selectively reflective powered optic
connecting first and second effectively parallel optical paths, the
first optical path providing for conveying image-bearing light from
the image generator to the selectively reflective powered optic and
the second optical path providing for conveying the image-bearing
light from the selectively reflective powered optic to the eyebox,
first and second selectively reflective surfaces each encountering
the image-bearing light along the first and second optical paths,
the first selectively reflective surface providing for conveying
the image-bearing light from the image generator to the second
selectively reflective optic and from the second selectively
reflective optic to the selectively reflective powered optic along
the first optical path and providing for conveying the
image-bearing light from the selectively reflective powered optic
to the second selectively reflective surface along the second
optical path, and the second selectively reflective surface
providing for conveying the image-bearing light from the first
selectively reflective surface back to the first selectively
reflective surface along the first optical path and providing for
conveying the image-bearing light from the first selectively
reflective surface to the eyebox along the second optical path.
12. The near-eye display of claim 11 in which the selectively
reflective powered optic and the first selectively reflective
surface have optical axes oriented substantially parallel to the
second optical path.
13. The near-eye display of claim 12 in which the second
selectively reflective surface also has an optical axis and the
optical axes of the first and second selectively reflective
surfaces are relatively inclined by an angle of less than 45
degrees.
14. The near-eye display of claim 13 in which the second
selectively reflective surface is oriented with respect to the
first selectively reflective surface through an angle between 25
degrees and 35 degrees.
15. The near-eye display of claim 11 in which the first and second
selectively reflective surfaces are supported by facets of a
prismatic waveguide that also includes an entrance facet along the
first optical path from the image generator oriented substantially
normal to the first optical path at the entrance facet.
16. The near-eye display of claim 15 in which the first selectively
reflective surface reflects the image-bearing light within the
prismatic waveguide by a mechanism of total internal
reflection.
17. The near-eye display of claim 15 further comprising a
supplemental prism having an adjoining facet adjacent to the second
selectively reflective surface and an exit facet oriented parallel
to the first selectively reflective surface.
18. The near-eye display of claim 17 in which the selectively
reflective powered optic, the first selectively reflective surface
supported by the prismatic waveguide, and the exit facet of the
supplemental prism all have optical axes oriented parallel to the
second optical path to the eyebox.
19. The near-eye display of claim 18 in which a see-through optical
path is located in parallel with the second optical path for
conveying ambient light through the selectively reflective powered
optic, the first and second selectively reflective surfaces
supported by the prismatic waveguide, and through the entrance and
exit facets of the supplemental prism to the eyebox.
20. The near-eye display of claim 11 in which the selectively
reflective powered optic is a reflective powered hologram.
21. The near-eye display of claim 20 in which the first selectively
reflective surface is a reflective unpowered hologram.
22. The near-eye display of claim 11 in which a see-through optical
path is located in parallel with the second optical path for
conveying ambient light through the selectively reflective powered
optic and the first and second selectively reflective surfaces to
the eyebox.
23. The near-eye display of claim 11 in which the first selectively
reflective surface provides for conveying the image-bearing light
(a) by reflection along the first optical path from the image
generator to the second selectively reflective surface, (b) by
transmission along the first optical path from the second
selectively reflective surface to the selectively reflective
powered optic, and (c) by transmission along the second optical
path from the selectively reflective powered optic to the second
selectively reflective surface.
24. The near-eye display of claim 23 in which the second
selectively reflective surface provides for conveying the
image-bearing light (a) by reflection along the first optical path
from the first selectively reflective surface back to the first
selectively reflective surface and (b) by transmission along the
second optical path from the first selectively reflective surface
to the eyebox.
25. A compound display and imaging device for displaying virtual
images from within an eyebox and for imaging external views from a
perspective of the eyebox comprising a camera, a selectively
reflective powered optic, and first and second selectively
reflective surfaces, the selectively reflective powered optic
providing for projecting virtual images from an image generator
along a display optical pathway to an eyebox having a field of view
within which the virtual images are visible, the first and second
selectively reflective surfaces each providing for conveying
display light along the display pathway from the image generator to
the selectively reflective powered optic and from the selectively
reflective powered optic to the eyebox, the camera providing for
imaging the external views along an image pathway through the
selectively reflective powered optic, the first and second
selectively reflective surfaces each providing for conveying image
light along the image pathway from the selectively reflective
powered optic to the camera, and the image pathway between the
second selectively reflective optic and the selectively reflective
powered optic being aligned with the display pathway between the
selectively reflective powered optic and the eyebox so that the
external views imaged by the camera are aligned with the virtual
images that are visible from within the eyebox.
26. The compound display and imaging device of claim 25 in which a
see-through pathway is aligned with both (a) the image pathway
between the second selectively reflective optic and the selectively
reflective powered optic and (b) the display pathway between the
selectively reflective powered optic and the eyebox so that
external views apparent from within the eyebox correspond to the
external views that are imaged by the camera.
27. The compound display and imaging device of claim 25 in which
the first selectively reflective optic conveys display light along
the display pathway to the second selectively reflective optic by
one of reflection or transmission and conveys image light along the
image pathway to the second selectively reflective optic by the
other of the reflection or transmission.
28. The compound display and imaging device of claim 27 in which
the second selectively reflective optic conveys both (a) the
display light along the display pathway to the selectively
reflective powered optic and (b) the image light along the image
pathway from the selectively reflective powered optic.
29. The compound display and imaging device of claim 25 further
comprising a prismatic waveguide assembly including a display
entrance facet along the display pathway and an image entrance
facet along the image pathway.
30. The compound display and imaging device of claim 29 in which
the first and second selectively reflective surfaces are supported
on facets of the prismatic waveguide assembly that are relatively
inclined through an angle of less than 45 degrees.
31. The compound display and imaging device of claim 30 in which
the prismatic waveguide assembly includes an inner supplemental
prism having an adjoining facet adjacent to the second selectively
reflective surface and an inner face facet oriented parallel to the
first selectively reflective surface.
32. The compound display and imaging device of claim 31 in which
the prismatic waveguide assembly includes an outer supplemental
prism having an adjoining facet adjacent to the selectively
reflective powered optic and an outer face facet oriented parallel
to the inner face facet.
33. The compound display and imaging device of claim 25 in which
the second selectively reflective surface is a
polarization-sensitive beamsplitter that reflects one orientation
of polarized light and transmits another orientation of polarized
light.
34. The compound display and imaging device of claim 33 in which
the polarization-sensitive beamsplitter reflects the image light
from the external view toward the camera, reflects the display
light from the image generator toward the selectively reflective
powered optic, and transmits the display light from the selectively
reflective powered optic toward the eyebox.
35. The compound display and imaging device of claim 34 further
comprising a polarization modifier for changing the orientation of
the polarized light located between the first selectively
reflective surface and the selectively reflective powered
optic.
36. The compound display and imaging device of claim 25 in which
the camera includes a focusing optic for focusing the external
views within the camera, and the selectively reflective powered
optic transmits the image light along the image pathway to the
camera without contributing focusing power.
37. A near-eye augmented reality device comprising an image
generator, a camera, and a selectively reflective powered optic,
the selectively reflective powered optic providing for projecting
virtual images from the image generator along a display optical
pathway to an eyebox having a field of view within which the
virtual images are visible, the camera providing for imaging
external views along an image pathway through the selectively
reflective powered optic, a see-through pathway extending through
the selectively reflective powered optic to the eyebox for
transmitting the external views to the eyebox, a portion of the
image pathway through the selectively reflective powered optic
being aligned with a portion of the display pathway between the
selectively reflective powered optic and the eyebox so that the
external views imaged by the camera are aligned with the virtual
images that are visible from within the eyebox, and a portion of
the image pathway through the selectively reflective powered optic
being aligned with the see-through pathway to the eyebox so that
the external views apparent from within the eyebox correspond to
the external views that are imaged by the camera.
38. The device of claim 37 further comprising a first selectively
reflective surface that reflects light along one of the image
pathway and the display pathway and transmits light along the other
of the image pathway and the display pathway for directing light to
the camera along the image pathway and directing light from the
image generator along the display pathway.
39. The device of claim 38 further comprising a second selectively
reflective surface that reflects light along one of the image
pathway and the see-through pathway and transmits light along the
other of the image pathway and the see-through pathway for
directing light to the camera along the image pathway and directing
light to the eyebox along the see-through pathway.
40. The device of claim 39 in which light from the image generator
twice encounters the first selectively reflective optic en route to
the eyebox and light from the external views twice encounters the
first selectively reflective optic en route to the camera.
Description
TECHNICAL FIELD
Near-eye displays, which include helmet-mounted, head-mounted, and
video eyewear displays, project virtual images generated by
microdisplay engines into viewers' eyes. Augmented reality near-eye
displays incorporate computer vision systems and project virtual
computer-generated imagery atop see-through views of the ambient
environment.
BACKGROUND OF THE INVENTION
Near-eye displays, particularly those that also provide see-through
views of the ambient environment, incorporate powered optics for
forming virtual images without unduly obstructing views of the
ambient environment. Some such displays fold light paths to the
powered optics out of the line of sight to the ambient environment
and in others, the powered optics are at least partially
transparent to light from the ambient environment.
The powered optics folded out of the line of sight generally add to
another dimension of the displays, particularly to the thickness of
the displays. Such additional thickness is often undesirable.
Near-eye displays are generally formed as thin as possible to more
closely replicate the styles of other eyewear.
The powered optics that are located along the line of sight are at
least partially transmissive to ambient light but are generally
oriented off axis to improve overall light efficiency and to reduce
thickness requirements of other display optics for directing
image-bearing light to the powered optics. The focusing power of
the powered optics is expressed under reflection. To preserve a
natural view of the ambient environment, either an additional optic
is required to undo the focusing power under transmission or the
powered optic is formed as a holographic optical element that
transmits ambient light largely undisturbed. The off-axis
orientation of the in-line powered optics often requires
corrections for both image distortion and chromatic aberration.
SUMMARY OF THE INVENTION
The invention among it preferred embodiments, features a near-eye
display with a selectively reflective powered optic (also meant to
be selectively transmissive as well) oriented nominally normal to a
line of sight to the ambient environment. Optical paths to and from
the selectively reflective powered optic effectively overlap. That
is, although the optical path to the selectively reflective powered
optic is folded to locate an image generator out of the line of
sight, the image generator and the selectively reflective powered
optic both remain nominally normal to local portions of the optical
path between them. The common optical alignment between the image
generator and the selectively reflective powered optic reduces
issues of image distortion and chromatic aberration, largely by
maintaining rotational symmetry.
In addition, the folded light path to the selectively reflective
powered optic allows the image generator or its relayed image to be
inclined (i.e., effectively inclined) to a thickness direction of
the near-eye display along the line of sight. The inclined
orientation of the image generator or its relayed image enables the
construction of a thinner, i.e., more compact, near-eye
display.
One version of a near-eye display in accordance with the invention
projects virtual images from an image generator to an eyebox within
which the virtual images can be seen by a viewer. A selectively
reflective powered optic connects first and second optical paths.
The first optical path conveys image-bearing light from the image
generator to the selectively reflective powered optic, and the
second optical path conveys the image-bearing light along a line of
sight from the selectively reflective powered optic to the eyebox.
First and second selectively reflective surfaces fold the first
optical path with respect to the second optical path to locate the
image generator out of the line of sight to the eyebox. The image
generator is effectively inclined to the line of sight to the
eyebox for reducing a thickness of the near-eye display, and the
selectively reflective powered optic is oriented nominally normal
to local overlapping portions of the first and second optical paths
at the selectively reflective powered optic for reducing image
distortion.
Preferably, the image generator is also oriented nominally normal
to a local portion of the first optical path at the image generator
for reducing image distortion. The first selectively reflective
surface and the selectively reflective powered optic have optical
axes preferably oriented substantially parallel to the line of
sight along the second optical path. The second selectively
reflective surface has an optical axis preferably oriented with
respect to the axis of the first selectively reflective surface
through an angle of less than 45 degrees and more preferably
between 25 degrees and 35 degrees.
The selectively reflective powered optic is preferably a
holographic optic arranged for focusing the image-bearing light
within the eyebox and transmitting ambient light along the line of
sight to the eyebox. The second selectively reflective surface
preferably includes a polarization-sensitive beamsplitter, and a
polarization modifier is preferably located between the first
selectively reflective surface and the selectively reflective
powered optic. The first and second selectively reflective surfaces
are preferably unpowered optical surfaces.
Another version of a near-eye display for projecting virtual images
from an image generator to an eyebox within which the virtual
images can be seen by a viewer includes a selectively reflective
powered optic connecting first and second effectively parallel
optical paths (i.e., paths that would be parallel if unfolded from
reflection). The first optical path conveys image-bearing light
from the image generator to the selectively reflective powered
optic, and the second optical path conveys the image-bearing light
from the selectively reflective powered optic to the eyebox. First
and second selectively reflective surfaces each encounter the
image-bearing light along the first and second optical paths. The
first selectively reflective surface conveys the image-bearing
light from the image generator to the second selectively reflective
optic and from the second selectively reflective optic to the
selectively reflective powered optic along the first optical path.
In addition, the first selectively reflective surface conveys the
image-bearing light from the selectively reflective powered optic
to the second selectively reflective surface along the second
optical path. The second selectively reflective surface conveys the
image-bearing light from the first selectively reflective surface
back to the first selectively reflective surface along the first
optical path and conveys the image-bearing light from the first
selectively reflective surface to the eyebox along the second
optical path.
Preferably, facets of a prismatic waveguide support the first and
second selectively reflective surfaces. An entrance facet of the
prismatic waveguide is preferably oriented nominally normal to the
first optical path at the entrance facet. The first selectively
reflective surface preferably reflects the image-bearing light
within the prismatic waveguide by a mechanism of total internal
reflection.
For viewing the ambient environment along the second optical path,
a supplemental prism can be provided with an adjoining facet
adjacent to the second selectively reflective surface and an inner
face facet oriented parallel to the first selectively reflective
surface. Preferably, the selectively reflective powered optic, the
first selectively reflective surface supported by the prismatic
waveguide, and the inner face facet of the supplemental prism all
have optical axes oriented parallel to the second optical path to
the eyebox.
A version of a compound display and imaging device in accordance
with the invention for both displaying virtual images from within
an eyebox and for imaging external views from a perspective of the
eyebox includes a camera, a selectively reflective powered optic,
and first and second selectively reflective surfaces. The
selectively reflective powered optic projects virtual images from
an image generator along a display optical pathway to an eyebox
having a field of view within which the virtual images are visible.
The first and second selectively reflective surfaces each convey
display light along the display pathway from the image generator to
the selectively reflective powered optic and from the selectively
reflective powered optic to the eyebox. The camera images the
external views along an image pathway through the selectively
reflective powered optic. The first and second selectively
reflective surfaces each convey image light along the image pathway
from the selectively reflective powered optic to the camera. The
image pathway between the second selectively reflective optic and
the selectively reflective powered optic is aligned with the
display pathway between the selectively reflective powered optic
and the eyebox so that the external views imaged by the camera are
aligned with the virtual images that are visible from within the
eyebox.
Preferably, a see-through pathway is aligned with both (a) the
image pathway between the second selectively reflective optic and
the selectively reflective powered optic and (b) the display
pathway between the selectively reflective powered optic and the
eyebox so that external views apparent from within the eyebox
correspond to the external views that are imaged by the camera. The
first selectively reflective optic preferably conveys display light
along the display pathway to the second selectively reflective
optic by one of reflection or transmission and preferably conveys
image light along the image pathway to the second selectively
reflective optic by the other of the reflection or transmission.
The second selectively reflective optic preferably conveys both (a)
the display light along the display pathway to the selectively
reflective powered optic and (b) the image light along the image
pathway from the selectively reflective powered optic.
A prismatic waveguide assembly within the compound display and
imaging device preferably includes a display entrance facet along
the display pathway and an image entrance facet along the image
pathway. The first and second selectively reflective surfaces are
preferably supported on facets of the prismatic waveguide assembly
that are relatively inclined through an angle of less than 45
degrees and more preferably between 25 degrees and 35 degrees. An
inner supplemental prism of the prismatic waveguide assembly
preferably includes an adjoining facet adjacent to the second
selectively reflective surface and an inner face facet oriented
parallel to the first selectively reflective surface. An outer
supplemental prism of the prismatic waveguide assembly preferably
includes an adjoining facet adjacent to the selectively reflective
powered optic and an outer face facet oriented parallel to the
inner face facet.
The second selectively reflective surface is preferably a
polarization-sensitive beamsplitter that reflects one orientation
of polarized light and transmits another orientation of polarized
light. For example, the polarization-sensitive beamsplitter can be
arranged to reflect the image light from the external view toward
the camera, reflect the display light from the image generator
toward the selectively reflective powered optic, and transmit the
display light from the selectively reflective powered optic toward
the eyebox. The camera preferably includes a focusing optic for
focusing the external views within the camera, and the selectively
reflective powered optic preferably transmits the image light along
the image pathway to the camera without contributing focusing
power.
A version of near-eye augmented reality device in accordance with
the invention includes both a camera and a selectively reflective
powered optic. The selectively reflective powered optic projects
virtual images from an image generator along a display optical
pathway to an eyebox having a field of view within which the
virtual images are visible. The camera images external views along
an image pathway through the selectively reflective powered optic.
A see-through pathway extends through the selectively reflective
powered optic to the eyebox for transmitting the external views to
the eyebox. A portion of the image pathway through the selectively
reflective powered optic is aligned with a portion of the display
pathway between the selectively reflective powered optic and the
eyebox so that the external views imaged by the camera are aligned
with the virtual images that are visible from within the eyebox. A
portion of the image pathway through the selectively reflective
powered optic is aligned with the see-through pathway to the eyebox
so that the external views apparent from within the eyebox
correspond to the external views that are imaged by the camera.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a diagrammatic top view of a near-eye display in
accordance with the invention.
FIG. 2 is a diagrammatic top view of a compound display and imaging
device 60 in accordance with the invention.
FIG. 3 is a similar diagrammatic top view of the display of FIG. 1
simplified for showing orientations and relationships with respect
to paraxial rays propagating through the display.
DETAILED DESCRIPTION OF THE INVENTION
A near-eye display 10, as depicted in FIG. 1, includes an image
generator 12 for producing a succession of images, such as video
images, that are projected as virtual images into an eyebox 14. The
image generator 12, which can take a number of forms, preferably
combines a spatial light modulator 16 with an illuminator 18 that
uniformly illuminates the spatial light modulator 16. The
illuminator 18 preferably includes a light source 17, which can be
formed by one or more light emitting diodes or other known sources
including lamps, and a condenser 19 that collects light from the
source 17 and evenly illuminates the spatial light modulator 16.
Light patterns are produced within the spatial light modulator 16
by differentially propagating light on a pixel-by-pixel basis in
accordance with a video input signal from a video source (not
shown). For example, the spatial light modulator 16 can comprise a
controllable array of liquid crystal diodes functioning as
individually addressable pixels for producing desired light
patterns in response to the video signal. Other spatial light
modulators useful for purposes of the invention include grating
light valve (GLV) technologies and digital light processing (DLP)
technologies such as digital micromirror devices (DMDs). The
spatial light modulator 16 and illuminator 18 can be replaced by
self-illuminating image generators in which the addressable pixel
elements are themselves individually controllable light sources,
such as organic light-emitting diode (OLED) technologies.
Within the near-eye display 10, the output of the image generator
12 is effectively located within an object plane 20, which is
intended to be projected as a magnified virtual image within the
eyebox 14. Light emitted from the image generator 12 enters a
prismatic waveguide 22 through an entrance facet 24 that is
oriented in parallel with the object plane 20 so that chief rays
from the object plane 20 or at least the paraxial rays encounter
the entrance facet 24 at near normal incidence.
Light emitted from the image generator 12 propagates along a first
optical path 26 through the prismatic waveguide 22 to a selectively
reflective powered optic 30, which focuses the light from the image
generator 12 by reflection along a second effectively parallel
optical path 28 through the prismatic waveguide 22 to the eyebox
14. The focal power of the selectively reflective powered optic 30
projects a magnified virtual image of the object plane 20, which is
viewable from within the eyebox 14. The selectively reflective
powered optic 30 is oriented substantially normal to local portions
of first and second optical paths 26 and 28, i.e., the optical axis
31 of the selectively reflective powered optic 30 is aligned with
the first and second optical paths 26 and 28 along their opposing
directions of incidence and reflection at the selectively
reflective powered optic.
Preferably, the selectively reflective powered optic 30 is formed
as a reflective volume hologram arranged for focusing selected
wavelengths of light. The selected wavelengths preferably
correspond to a red-green-blue (RGB) color combination output by
the image generator 12. Image-bearing light in the selected colors
is reflected and focused along the second optical path 28. The
remaining wavelengths of visible light, which include other
wavelengths red, green, and blue light beyond the coherent bands
over which the volume hologram is formed, transmit through the
volume hologram largely undisturbed.
Before reaching the selectively reflective powered optic 30 along
the first optical path 26, first and second selectively reflective
surfaces 34 and 36 fold image-bearing light from the image
generator 12 out of physical alignment with the eyebox 14. Except
for the two reflections at the selectively reflective surfaces 34
and 36, which do not appreciably alter or otherwise distort the
wavefront shape of the image-bearing light, the first and second
optical paths 26 and 28 remain effectively optically aligned. In
other words, if the first optical path 26 were to be physically
unfolded, the first optical path from the image generator 12 to the
selectively reflective powered optic 30 would overlie the second
optical path 28 from the selectively reflective powered optic 30 to
the eyebox 14. Since the object plane 20 lies substantially normal
to the first optical path 26 and the first and second optical paths
34 and 36 are effectively optically aligned with one another, the
virtual image is formed without distortion or any requirement for
correcting distortion along either of the two optical paths 26 and
28.
The first and second selectively reflective surfaces 34 and 36 are
supported by or otherwise formed by facets 42 and 44 of the
prismatic waveguide 22. The first selectively reflective surface 34
is formed on or by the facet 42 and exhibits selective reflectivity
by the mechanism of total internal reflection (TIR), which exploits
a difference between the refractive index of the prismatic
waveguide 22 and the refractive index of the local environment
adjacent to the facet 42. Coatings or other modifications to the
facet 42 can be used to influence the reflective properties of the
first selectively reflective surface 34. Preferably light from the
image generator 12 first encounters the first selectively
reflective surface 34 along the first optical path 26 at angles of
incidence greater than the critical angle above which the light is
totally internally reflected.
The second selectively reflective surface 36 is preferably
fashioned as a polarization-sensitive beamsplitter 40 supported on
the facet 44 of the prismatic waveguide 22. At least a portion of
the image-bearing light from the image generator 12 last reflected
from the first selectively reflective surface 34 is further
reflected by the second selectively reflective surface 36 along the
first optical path 26 through the first selectively reflective
surface 34 to the selectively reflective powered optic 30. En route
top the selectively reflective powered optic 30 the image-bearing
light encounters both the first selectively reflective surface 34
and a polarization modifier 46 at a nominal normal incidence. The
near zero incidence angle at which the image-bearing light
encounters the first selectively reflective surface 34 is well
below the critical angle required to support total internal
reflection within the prismatic waveguide 22. So, while the first
encounter of the image-bearing light with the first selectively
reflective surface 34 along the first optical path 26 is
reflective, the second encounter of the image-bearing light with
the first selectively reflective surface 34 is along the first
optical path 26 is transmissive.
Instead of exploiting the mechanism of total internal reflection
(TIR) to support the function of selective reflectivity, the second
selectively reflective surface 36 in the form of the
polarization-sensitive beamsplitter 40 exploits the mechanism of
polarization to support the function of selective reflectivity. The
light emitted from the image generator 12 can be at least partially
polarized, especially if a liquid crystal array is used in
combination with orthogonal polarizers as the spatial light
modulator 16. The second selectively reflective surface 36 as a
polarization-sensitive beamsplitter is preferably arranged to
reflect the polarization orientation of the image-bearing light
from the image generator 12 and to transmit an orthogonal
orientation of polarization.
The polarization modifier 46, which is spaced from the first
selectively reflective surface 34 to preserve an air gap 48 or
other low-reflectivity medium required for sustaining total
internal reflection (TIR), modifies the polarization of the image
bearing light by relatively retarding one orthogonal polarization
component with respect to another through approximately .pi./2
radians. After being both reflected and focused by the selectively
reflective powered optic 30, the image-bearing light propagates
along the second optical path 28 through both the polarization
modifier 46 and the first selectively reflective surface 34 to the
second selectively reflective surface 36. Since the optical axis 31
of the selectively reflective powered optic 30 is aligned with
local portions of the first and second optical paths 26 and 28, the
focused image-bearing light reflected from the selectively
reflective powered optic 30 transmits through both the polarization
modifier 46 and the first selectively reflective surface 34 at near
normal incidence and well below the critical angle for TIR. The
second encounter of the image-bearing light with the polarization
modifier 46 relatively modifies the orthogonal polarization
components of the image-bearing light by another .pi./2 radians, so
the total modification from both encounters orthogonally transforms
the polarization of the image-bearing light. A one-quarter wave
plate retarder is preferably used to perform the two-step
polarization modification. The focused image-bearing light
propagating along the second optical path 28 transmits through the
second selectively reflective surface 36 (i.e., the
polarization-sensitive beamsplitter 40) as orthogonally rotated
polarized light en route to the eyebox 14.
While the entrance facet 24 is substantially normal to the local
portion of the first optical path 26 to minimize chromatically
sensitive refractive effects, the facet 44, on which the second
selectively reflective surface 36 is formed as the
polarization-sensitive beamsplitter 40 and through which the second
optical path 28 exits the prismatic waveguide 22, is not
substantially normal to the second optical path 28. Instead, the
second selectively reflective surface 36 is inclined to the first
selectively reflective surface 34 through an acute angle that is
preferably less than 45 degrees and more preferably between 25
degrees and 35 degrees. At 30 degrees, image bearing light entering
the prismatic waveguide 22 propagates parallel to the second
selectively reflective surface 36 (i.e., the facet 44) en route to
the first selectively reflective surface 34 (i.e., the facet 42)
for efficiently filling the prismatic waveguide 22.
A supplemental prism 50 having an adjoining facet 52 mated to the
polarization-sensitive beamsplitter on the selectively reflective
surface 36 on the facet 44 of the prismatic waveguide 22 and having
an exit facet 54 parallel to the selective reflective surface 32 on
the facet 42 of the prismatic waveguide minimizes chromatically
sensitive refractive effects on the image bearing light propagating
toward the eyebox 14. The minimized prismatic refraction also
avoids a shift in the viewing position of the projected virtual
image within the eyebox 14. To this end, the refractive index of
the supplemental prism 50 preferably matches the refractive index
of the prismatic waveguide 22.
The mating prisms, i.e., the prismatic waveguide 22 and the
supplemental prism 50, function together as a single plane parallel
plate with respect to a see-through pathway 56 in alignment with
the second optical path 28. However, the supplemental prism 50 and
the prismatic waveguide 22 are preferably mated together in an
offset position so that their combined thickness as a plane
parallel plate along the second optical pathway 28 and the
see-through pathway 56 is less than the sum of their individual
thicknesses. The offset between the prismatic waveguide 22 and the
supplemental prism 50 allows the entrance facet 24 to be sized
independently of the combined thicknesses of the prismatic
waveguide 22 and the supplemental prism 50 plate in front of a
viewer's eye.
Ambient light enters the near eye display 10 through the
selectively reflective powered optic 30, preferably in the form of
a volume hologram, and propagates along the see-through pathway 56
through the polarization modifier 46 and the mating prisms 22 and
50 and into the eyebox 14 in alignment with the image-bearing light
focused into the eyebox by the selectively reflective powered optic
30. The polarization-sensitive beamsplitter located between the
mating prisms 22 and 50 reflects a portion of the ambient light,
preferably so-called "S-polarized" light, which is prone to
reflections off ground oriented surfaces. Thus, the near-eye
display 10 functions similar to polarized sunglasses with respect
to ambient light while also projecting virtual images from the
image generator 12 that are visible within the eyebox 14.
A compound display and imaging device 60 for displaying virtual
images from within an eyebox 14 and for imaging external views from
a perspective of the eyebox 14 is disclosed in FIG. 2. Together
with known software within a processor 58 for processing
information imaged from the external views and for incorporating
the imaged information in some form, such as computer-generated or
computer-modified imagery, into the displayed virtual images, the
device 60 can be used as a mediated reality device. For example,
the imaged information can be processed for purposes of object
recognition and information about the recognized objects can be
incorporated into the displayed virtual images. Information can
also be gathered from the imaged external views that would not
normally be visible to a viewer using the device 60 (e.g., infrared
light), processed, and incorporated into the displayed images for
enhancing the viewer's view or other sensory appreciation of the
external environment.
A display portion of the device 60 is similar to the near-eye
display 10 of FIG. 1 except that the selectively reflective surface
34 is rendered selectively reflective by a volume hologram 62
instead of by the mechanism of total internal reflection (TIR). In
addition, since no gap is required to sustain TIR, the polarization
modifier 46 and the selectively reflective powered optic 30 (e.g.,
a powered volume hologram) can be moved alongside the volume
hologram 62. For sake of simplicity, features of the compound
display and imaging device 60 in common with the near-eye display
10 of FIG. 1 share the same reference numerals.
Three optical pathways are defined through the device 60: a display
pathway 64, an image pathway 66, and a see-through pathway 68. The
display pathway 64 corresponds to the first and second optical
paths 26 and 28 through the device 10 for projecting virtual images
that are visible within the eyebox 14. The image pathway 66 conveys
to a camera 70 external views corresponding at least in part to an
ambient view of the along the see-through pathway 68 to the eyebox
14. The see-through pathway 68 corresponds to the see-through
pathway 56 of the display 10 but is extended to accommodate
additional optics associated with the image pathway 66.
In addition to the structures in common with the display 10, the
device 60 includes a prismatic waveguide 72 and a supplemental
prism 74. The prismatic waveguide 72 is primarily intended for
diminishing refractive effects along the imaging pathway 66
associated with ambient light passing through the first selectively
reflective surface 34 on the facet 42 of the prismatic waveguide
22. The supplemental prism 74 is primarily intended for diminishing
refractive effects along the combined imaging and see-through
pathways 66 and 68 associated with ambient light passing through a
facet 76 of the prismatic waveguide 72. Alternatively, the
prismatic waveguide 72 and the supplemental prism 74 could be
combined into a single prismatic waveguide, particularly since the
facet 76 of the prismatic waveguide 72 is not required to perform
an independent optical function in the depicted embodiment. An
index matching adhesive 78 joins the prismatic waveguide 72 and the
supplemental prism 74 to the prismatic waveguide 22 and the
supplemental prism 50.
Ambient light along both the imaging pathway 66 and the see-through
pathway 68 enters the supplemental prism 74 through an entrance
facet 80 and passes through an interface between the facet 76 of
the prismatic waveguide 72 and an adjoining facet 82 of the
supplemental prism 74. An inner face facet 84 of the prismatic
waveguide 72 adjoins the selectively reflective powered optic 30
along at least part of its length and the index matching adhesive
78 couples the remaining common portions of the two prismatic
waveguides 22 and 72 and the two supplemental waveguides 50 and
74.
Light exiting the prismatic waveguide 72 along the imaging pathway
66 enters the prismatic waveguide 22 through various interfaces
including through a combination of the selectively reflective
powered optic 30, particularly as a powered hologram, the
polarization modifier 46, and the selectively reflective surface
34, particularly as a angular sensitive reflective hologram and
through a combination of the index matching adhesive 78 and the
selectively reflective surface 34.
The selectively reflective surface 36, particularly as a
polarizations-sensitive beamsplitter 40, reflects a portion of the
light along the imaging pathway back through the same interfaces
between the prismatic waveguides 22 and 72 en route to the camera
70. Substantially the entire remaining portion of the light is
transmitted through the polarization sensitive beamsplitter 40
along the see-through pathway 68 en route to the eyebox 14.
Along the imaging pathway 66, light exits the prismatic waveguide
72 through an exit facet 86 that is oriented normal to the imaging
pathway 66. The camera 70, which completes the imaging pathway 66,
includes a focusing optic 87 and a detector 89. The focusing optic
87 images views within the ambient environment onto the detector
89, which is located at an imaging plane. The detector 89 is
preferably a digital image capturing device such as a charge
coupled device (CCD) array. The processor 58 receives image
information captured by the camera 70.
Along the see-through pathway 68, ambient light exits the prismatic
waveguide 72 through the exit facet 54, which extends parallel with
the entrance facet 80. Thus, the device 60 functions largely as a
plane-parallel plate along the see-through pathway 68 for avoiding
prismatic or other refractive effects, at least with respect to the
chief rays (or at least paraxial rays of systems that depart more
significantly from telecentricity) transmitted through the device
60. The optical path portion 28 along the display pathway 64 is
aligned with and overlaps the see-through pathway 68 within the
prismatic waveguide 22 and is aligned with and overlaps the imaging
pathway within a portion of the prismatic waveguide 22 between the
first selectively reflective surface 34 and the exit facet 54. If
unfolded from reflection, all three pathways 64, 66, and 68 would
be aligned with each other along a common optical axis and
substantially centered within the eyebox 14.
The processor 58, which can have access to additional information
in memory or from other sources, such a global positioning system
data, processes the digital image information from the camera 70
taken largely along the line of sight of the see-through pathway
68. The processed information is preferably used to generate text
or graphics that are reproduced by the image generator 12 for
projection as virtual images that can be overlaid onto the viewer's
view of the external world along the same line of sight. The text
and graphics can overlay or reference particular features that are
visible along the see-through pathway 68 or other features that are
not visible or are only marginally visible to a viewer. To
precisely associate projected virtual images of text or graphics
with particular features in the external world, the images received
the camera 70 should be optically aligned and scaled to the images
reproduced by the image generator 12 and both the images received
by the camera 70 and the images reproduced by the image generator
12 should be optically aligned and scaled to the images of the
external world that are visible to a viewer along the see-through
pathway 68.
With reference to FIG. 3 depicting the propagation of paraxial rays
through the near-eye display 10 of FIG. 1 and assuming that (a) the
first selectively reflective surface 34 is oriented normal to the
optical axis 31 of the selectively reflective powered optic 30 and
(b) the second selectively reflective surface 36 reflects light
(i.e., at least the paraxial rays) along the same optical axis 31,
an incidence angle ".delta." at which the paraxial rays approach
the first selectively reflective surface 34 is equal to two times
an angle ".theta." at which the second selectively reflective
surface 36 is inclined to the first selectively reflective surface
34. As also apparent from FIG. 3, the object plane 20 of the image
generator 12 is inclined (i.e., an effective inclination of the
image generator 12) with respect to the optical axis 31 of the
selectively reflective focusing optic 30 and the see-through
pathway 68 through an angle equal to the complement of the
incidence angle ".delta.", which allows the display 10 to be
narrower in the direction of the see-through pathway 68. En route
to the first selectively reflective surface 34, the inclination of
the object plane 20 can reduce the local thickness of the display
by the Cosine function of the inclination angle.
The illustrated designs support inclination angles ".theta." of
less than 45 degrees for limiting the thickness of the devices 10
and 60 along the see-through pathway 68. Preferably, the
inclination angles ".theta." approach 30 degrees so that the
closest chief rays (or at least the paraxial rays) propagate from
the image generator 12 toward the first selectively reflective
surface 34 nearly parallel to the second selectively reflective
surface 36 for efficiently filling the prismatic waveguide 28.
Inclination angles of between 25 degrees to 35 degrees are
preferred so that the paraxial rays propagate toward a first
encounter with the first selectively reflective surface 34 within
15 degrees of the second selectively reflective surface 36.
Within these preferred bounds, accommodations can be made for
achieving desired ratios of optical path lengths between the first
and second optical paths 26 and 28 in keeping with a focal length
"F" of the selectively reflective focusing optic 30 and the desired
magnification of the design. Generally, the eyebox 14 is located at
approximately one focal length "F" from the selectively reflective
focusing optic 30 along the second optical path 28. The image
generator 12, or more specifically, the object plane 20 within
which the image generator 12 generates an object image, is
preferably located at an optical distance along the first optical
path 26 to the selectively reflective focusing optic 30 slightly
shorter than the focal length "F", so that the virtual image of the
object image appears to the viewer from within the eyebox 14 at a
distance of approximately three meters.
Although in the preceding FIGS. 1-3, the object plane 20 of the
image generator 12 is depicted coincident with a surface of the
spatial light modulator 16, the object image produced at the
spatial light modulator 16 or other image generating source can be
relayed into the position shown by relay optics (not shown). In
other words, the image generator 12 can be located remotely, and
the object images generated by the image generator 12 can be
relayed to a desired position at a predetermined optical path
length along the first optical path 26 to the selectively
reflective focusing optic 30.
The devices 10 or 60 illustrated above are preferably supported in
frames (not shown) for positioning the eyeboxes 14 at or near a
wearer's (i.e., viewer's) pupil. Similarly powered devices 10 or 60
can be mounted for presenting virtual images to both of a viewer's
eyes. A filter, such as a polarization modifier, can be positioned
near an entrance to the see-through pathway 68 to relatively adjust
the amount of ambient light reaching the eyebox 14 with respect to
the amount of image bearing light from the image generator 12
reaching the eyebox 14. Particularly with respect to the compound
display and imaging device 60, the image generator 12 and camera 70
can be arranged interchangeably. For example, image-bearing light
propagating along the first optical path 26 can be arranged for
transmitting through the first selectively reflective surface 34 en
route to the second selectively reflective surface 36, and ambient
light reflected from the second selectively reflective surface 36
can be reflected by the first selectively reflective surface 34 en
route to the camera 70. These and other modifications, additions,
and other changes will be apparent to those of skill in the art in
accordance with the overall teaching of this invention.
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